Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$146.43	6.630%	$156.1383	$156.14	$156.15	$156.10
Purchase #2	$122.69	13.502%	$139.2556	$139.26	$139.25	$139.30
Purchase #3	$131.79	3.477%	$136.3723	$136.37	$136.35	$136.40
Purchase #4	$144.52	12.593%	$162.7194	$162.72	$162.70	$162.70
Purchase #5	$99.35	11.770%	$111.0435	$111.04	$111.05	$111.00
Purchase #6	$27.46	10.276%	$30.2818	$30.28	$30.30	$30.30
Purchase #7	$138.74	3.734%	$143.9206	$143.92	$143.90	$143.90
7 purchase totals =	$810.98		$879.7315	$879.73	$879.70	$879.70